Signaling system



Patented Apr. I 8, 1930 um TA'EES rtur OFFICE RUSSELL s. OHL, or new YonK, n. Y.,ASSIG1\TOR T AMERICAN "IELEPHONEAND 'rnLE-- GRAPH corarAnY, A oonronn'rron on NEW YORK SIGNALING; SYSTEM Application filed October a, 1926. Serial No, 40,397;

This invention relates to signaling systems, and particularly to arrangements in such systemsfor faithfully reproducing original low, frequency signals from corresponding- 5 bands of signals of'high frequencyr It is well known that in order to attain good voice quality in voice frequency signaling systems when transmitting voice frequency signals in the form of high frequency energy 0 over a considerable distance, it is necessary to maintain the high frequency or carrier wave very constant in frequency. In order to receive anddetect the energy present in, for example, a single side band of such high frequency energy,it is necessary to introduce some local frequency which may be employedto beat with the side band in order that the low frequency signals may be faithfully reproduced. i r

A common practice for'receiving a 'high frequency modulated signal is first, to change the frequency of the signal to another frequency lowered in the frequency spectrum,

. which maybe amplified more easily than the first high frequency originally received, and

second, to detect the signal from the intermediate frequency. This is done by the. wellknown' means of beating the received high frequency signal with. the :unmodulated,

harmonic producer to produce a harmonic of 1 I g with particularity in the appended claims, the

the frequency of that oscillator to'be used as a local beating frequency to beat with an incoming side band of high frequency energy. In order to maintain'each of thelocal frequencies constant with, very narrow limits, a piezo-electric "device will be connected to each oscillator. Means are associated with each piez'o-electric device for carefully. ad

; l -fi itS Characteristic. frequency with-con One can readily sider able accuracy. Accordingly, the frequency of the oscillator to which the piezoelectric device is connected will similarly be varied in frequency in accordance with the variation inthe characteristic frequency of the piezoelectric device. The first local oscillator transmits a frequency which, when beaten with the incoming side band ofhigh frequency energy, produces an intermediate band of frequencies which iswell defined inthe frequency spectrum. The second oscillator, which is controlled andvaried as to its frequency by means of asimilar piezo-ele'ctric device, is employed tobeat with the intermediate band of frequencies so that the lOW frequency signals originally received by the system in the form of high frequency energy are faithfully detected and reproduced.

Accordingly, it is an object of this invention to associate the output of an oscillator with a band of high frequency energy so that by co'ntrollingan'd varying. the frequency of the oscillator as conditions. necessitate, the

band of signals will be accurately detected and reproduced. I I I Another of the objects of this invention'is 'to so relate a firstoscillator and a harmonic producer to means for receiving a band of high frequency energy that the harmonic producer will, produce a harmonic of the' frequency of the first oscillator, which is piezo-electrically controlled and varied as to its frequency, in orderthat an intermediate band of signals,corresponding to'the original signals, will be produced which may be further beaten withthe frequency of the second oscillator, similarly piezo-electrically controlled and varied as to its frequency, to

reproduce the original signals, Withgreater 1 accuracy than has heretofore beenpossible. While the invention will be-pointed out tem comprising an antenna N and ground is employed to receive a side band of very high frequency energy. This side band of high frequency energy is impressed upon the first detector D The reference characters 0 and O designate two oscillators, each sustaining oscillations of high frequency. Thesew oscillators may be of any well-known type, but ihiy l? p ef ably of he c um, tube yp Each oscillator may, of course, be of the untuned type and may of itself vary in frequency considerably from its characteristic frequency. In order to maintain the frequency of the oscillations sustained by the oscillators O and O constant within very narrow limits and in order to render the frequency characteristics of these oscillators adadjustable thumb screws T and T so that as these thumb screwsare moved inwardly or outwardly a corresponding change will take place in the distance between the respective piezoelectric crystal and the corresponding conductive electrode L or L Obviously the width of the dielectric, such, for examnple, as air between the conductive electrodes L, and L and the corresponding pieZo-electric crystals PE and PE may be changed by manipulation of the thumb screws T and T respectively. Each piezo-electric device may be located in a box or other container, which may preferably be made of hard rubber, bakelite, or other insulating material. Means may. also be provided with each piezoelectric device for accurately determining the displacement of its thumb screw. It isto be understood, however, that it is within the scope of this invention to provide any means whatsoever for rendering a fine adjustment .=of the space between any piezo-electriccrys tal and one or both of its conductive elec-- trodes SO'thil-t in effect the frequency characteristic of that piezo-electric-i crystal may be adjusted andvaried with considerable aci 'In anoscillator with which a piste-electric device is-associated, which comprises a piezoelectric-crystal vibratmg between conductive .quency-of oscillations sustained by the oscil-. co

electrodes, it has been found that; the frelater maybe controlled and variedasfto fre quency by. adjusting the-sine of the gap existing-between the-piezoelectric crystal and -'-..-its-.conductive electrodes Generallyyas the space between the crystal and. its-conduc- :t en mdesnhanse ra eqm iioiisiinschange is produced in the frequency of the oscillations sustained by the oscillator. More particularly, as the distance between the piezo-electric crystal and its conductive elec trodes is increased, the frequency of the oscillations sustained by the oscillator will, under. normal conditions, also be increased, and vice versa. This is exactly what takes place when the piezo-electric devices comprising the piezoelectric crystals PE and PE and the conductive electrodes L and L and L and L respectively, are associated with the oscillators O and Briefly, the frequency of the oscillations sustained by the oscillators O and 0 may be controlled and varied by these piezo-electric devices with precision.

Oscillations sustained by theoscillator O controlledand varied as to frequency by the associated piezo-electric device, are transmitted to a harmonic producer HP which is employed to produce a harmonic of the frequency of wave sustained by the oscillator O This harmonic producer may be of any wellknown type, but is prefer-ablyof the wellknown vacuum tube type. It may produce any desired harmonic of the oscillations sustained by the oscillator 0 This harmonic is transmitted to the detector -D and is employed to beat with the incoming side band of high frequency energy This detector D may be of any well-known type, but it is also preferably of a vacuum tube type. By beating the frequency of the harmonic with the incoming side band of high frequency energy, another band of signals is produced which lies in a different position in the frequency spectrum. The output of the detector D is then transmitted to an intermediate frequency amplifier A which is employed 7 to amplify the band of signals transmitted by the detector D This intermediate frequency amplifier may, of course, be of any wellknown type, but it is also preferably of the vacuum tube type. After amplification by the amplifier A, the intermediate band of signals is impressed upon asecond detector D The frequency sustained by the oscillator 0 which is controlled and varied as to frequency by means of the piezo-electric device connected thereto, is transmitted to the second detector D which may also be of any well-known type but which is preferably, of the vacuum tube type. The second detector D beats the frequency of the oscillator 0 with the band of signalstransmitted by the ,amplifier A. Accordingly, the original signals Which-arereceived by thev antenna N in the form of a side band of high frequency energy are faithfully received by a head set R. It willbe fairly obvious that if the oscil- 4 lations'of the oscillators Q and Q were not each controllable andvariableasto their; frequencies it by; some such device-as is-shown ,h rei i -ie.-;- a Piezo l ctr c evice:- t icrigmal signals ildnet befiaithfil y reproduced. By associating piezo-electric devices with these oscillators it is possible to maintain a higher quality in transmission than has heretofore been possible. i

It will be understood that while only two oscillators have been shown herein, each beating with a band of signals, any number of oscillators may be similarly associated with a signaling system, the characteristic frequencies V of these oscillators additively approximating the frequency of the wave which may be considered adjacent to the received band of signals. It will be understood that piezoelectric means may be associated with each of these oscillators for bringing their additive effects into exactsynchronism with the high frequency wave assumed to be adjacent to the received band of signals.

It will also be understood that while this system has been shown herein, for the pur pose of illustration, as a double detection system, the principles of this invention may be applied to numerous other systems and to various embodiments of such systems without departing from the spirit of the invention and the scope of the appended claims.

What is claimed is:

1. In a signaling system, the combination of means for receiving a band of signals of high frequency, two local oscillators, piezo- 7 electric means for controlling and varying the frequency of'said oscillators, means for producing a harmonic of the frequency of the first oscillator which will be similarly controlled and varied as to frequency by said piezo-electric means, means for beating said piezo-electrically controlled and varied harmonic of the first oscillator with the band of signals to produce a corresponding band of signals lowered in the frequency spectrum, and means for beating the piezo-electrically controlled and varied frequency of the second oscillator with the band of signals lowered in the frequency spectrum in order to accurately reproduce the original signals.

2. In a signaling. system, the combination of means for receiving a band of signals of high frequency representing speech, first and second oscillators, piezo-electric means coupled to each oscillator for controlling the frequency of sustained oscillations, means for varying the vibratory period of the piezoelectric means coupled to each oscillator to produce a corresponding variation in the frequency of the oscillations sustained thereby, means for beating the piezo-electrically controlled and varied frequency of the first oscillator with the received band of signals so as to produce a corresponding band of signals changed in the frequency spectrum,

and means for beating the piezo-electrically controlled and varied frequency of the second oscillator with the latter band of signals changed in the frequency spectrum to faith- I fully reproduce the speech signals.

3. In a signaling system, the combination of means for receiving a side band of high electric means connected with each oscillator for controlling the frequency of the generated wave, said piezo-electric means including a screw-threaded member for varying its effective period of vibration in order to maintain the additive effect of both of the generated waves in synchronismwith the carrier wave corresponding to the received side band, means for beating one of the piezoelectrically controlled and varied waves withthe received side band to produce another bandof signals changed in the frequency spectrum and characteristic of the same voice frequency signals, and means for beating the other of the piezo-electrically controlled and varied waves with the latter band of signals inorder that the voice frequency signals may be faithfullly derived and reproduced.

In testimony .wherof, I have signed my name to this specification this 6th day of October, 1926. I I

, RUSSELL S. OHL. 

